In the diseased heart, the high risk of Sudden Cardiac Death has traditionally been ascribed to increased tissue heterogeneity associated with disease-related structural and electrical remodeling, which predisposes cardiac tissue to electrical wavebreak and ventricular fibrillation (VF). However, recent studies indicate that dynamic wave instability operates synergistically with pre-existing tissue heterogeneity to promote wavebreak. Dynamic wave stability is regulated by multiple factors, including electrical restitution, intracellular Ca (Cai) cycling, cardiac memory, and electrotonic currents. The goal of this project is to combine mathematical and experimental biology to develop novel therapeutics for VF, based on altering global voltage-Cai dynamics to increase wave stability. To develop this concept, the first goal is to overcome shortcomings of existing action potential (AP) models by incorporating realistic voltage-Cai cycling dynamics into AP models for normal and failing adult rabbit ventricular myocytes and neonatal rat ventricular myocytes, validated experimentally against patch clamp and Cai imaging data. The second aim is to explore interactions between voltage-Cai dynamics and tissue heterogeneity experimentally in the simplified 2D geometry of cultured neonatal rat ventricular tissue monolayers, complementing the theoretical studies in Project 2. The third aim is to use the developed AP models in combination with biological experiments to develop and evaluate specific molecular targets for suppressing wave instability driven by Vm-Cai cycling dynamics, in collaboration with Projects 2, 3 and 4. Based on preliminary studies showing that the L-type Ca current sits at a critical focal point controlling multiple aspects of dynamic wave stability, we will focus on modification of this current as the initial strategy. We will utilize mathematical modeling, patch clamp studies, optical mapping, and adenoviral gene transfer into cultured neonatal rat ventricular monolayers and, in collaboration with Project 3, intact rabbit hearts as a proof-of-concept strategy for gene therapy.